From: jklowden@speakeasy.net   
      
   On Thu, 25 Oct 2012 14:06:44 -0700 (PDT)   
   fmatthew5876  wrote:   
      
   > Why waste time with bit shifts and ors? You could do something like   
   > this:   
   >   
   > //assume the data is big endian   
   > inline uint32_t unpackbe32(unsigned char* buf) {   
   >   union {uint32_t u32; uint8_t u8[4] } u;   
   > #if LITTLE_ENDIAN   
   >   u.u8[3] = buf[0];   
   >   u.u8[2] = buf[1];   
   >   u.u8[1] = buf[2];   
   >   u.u8[0] = buf[3];   
   > #else   
   >   u.u8[0] = buf[0];   
   >   u.u8[1] = buf[1];   
   >   u.u8[2] = buf[2];   
   >   u.u8[3] = buf[3];   
   > #endif   
   >   return u.u32;   
   > }   
      
   Can you?  I've heard that called type-punning.  Section 9.5 of the   
   standard says, "the value of at most one of the non-static data members   
   can be stored in a union at any time."  IOW, you can only read what you   
   wrote; you can't assume u32 and u8 are at the same address.   
      
   Me, I would call htonl or similar.  I haven't seen a serialization   
   library I like yet.   
      
   --jkl   
      
      
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